Parameter space for the evolution of the Doppler factor index d as a function of the jet expansion index ρ and the spectral slope s for the different region A–D for three different jet configurations, The first column assumes an adiabatic jet (k = k_ad = 2(s + 2)/3) and equipartition between the magnetic energy density and the kinetic energy of the relativistic particles, represented by b = b_eq = (s + 2)/3. The second and third columns show the evolution of d for an adiabatic jet (k = k_ad) and decreasing magnetic field b = 1 or b = 2, respectively. The iso-contours in each panel show the allowed range for the exponent d (δ ∝ r ^− ρd) and the gray shaded area the range for the parameter ρ (R ∝ r^ρ), with different scales for parameter ρ in region B. For more details see text.